Building A Custom Mauser Rifle–Part 1

Ken Brooks

by Ken Brooks, AGI Gunsmithing Instructor and
owner of  PISCO Gunsmithing in Oregon.

There are many reasons for “sporterizing” a military Mauser, but the belief that the result will be less costly than a new rifle at Walmart is not one of them.

A custom Mauser rifle can bring great pride of ownership. Owners appreciate, and have a passion for, the history of Mauser rifles. They also enjoy having one built to their specifications, whether for practical purposes, such as hunting, or simply to enjoy owning a beautiful rifle. I will explain the steps needed in such a project.


There are a couple of things to realize before starting. First, sporterizing a military rifle will not be cheap. It will easily exceed a $500 budget; for that much money an off-the-shelf commercial hunting rifle would be more cost-effective. While you don’t necessarily need to spend $85,000 like the higher-end models, it will be a considerable investment. And it is, truly, an investment. It’s important for your customers to know this upfront.

Ken with two versions of '98 Mauser sporters in front, and another on the wall top left.

Ken with two versions of ’98 Mauser sporters in front, and another on the wall top left.

Second, choose carefully when selecting your base gun. If you find a Mauser in good condition, with a good barrel, and matching serial numbers, you should not do anything to that rifle. It would be a highly-valuable collector’s item and would likely be worth far more than if it were sporterized. However, if you have a rifle where the bore’s been shot out or the sights are missing, and the only thing really left is a serviceable action worth $150-200, that would be a good choice as a base for a custom gun.

Customer First

The first step is communicating with the customer. You want to make sure the customer is aware of what will be involved in the project. The best customer is one who is educated on the strengths and weaknesses of the Mauser action and knows exactly what he wants. At the very least the customer should have an idea of the rifle’s purpose. This will help you build a rifle that meets the customer’s needs. A happy, satisfied customer is good for business.


The quality of a Mauser action can vary depending on the manufacturer. I prefer the CZs, the BRNOs, and virtually any of the German variants. The Austrian actions are good, as well. Of course, original Mauser actions are going to be highly collectible stuff, so you may not want to alter them. There seems to be a lot of CZs on the market right now. The CZ-24 is a great action to build on. Belgian products are also good.

There are commercial 98s as well. Modifications for civilian use have already been “built-in” to these actions, so there’s not as much to do to as there would be on a military action.

The BRNOs are the ones I had to do a lot of machining on to get them to feed. They feed the original 8x57mm (or 7×57, or .257 Roberts) great, but if you go to alter it to something else you will probably need to do a little bit of work. I don’t want to advise you to avoid them, but be aware you may have to do more work on the feed-rail, especially if you’re going to a magnum cartridge.

There are predominantly two different types of Mauser actions, small rings and large rings. The small rings are almost always cock-on-close, which means you have to push the bolt forward and rotate it down to compress the firing pin spring and lock the bolt into place. With the large ring, or Model 98, starting with the bolt down and closed, opening the bolt cams the cocking piece back and puts it into the cocked position. When you close it there’s no compression of the spring, so it’s much easier.

Another difference is that the small ring is smaller in diameter at the front where the barrel screws in. It’s not quite as strong as the 98. The internal mechanism of the large ring has an internal ring on the inside that encases the bolt head, which makes the 98 stronger as well. The small rings are not recommended for any magnums. I would suggest you stay away from the small ring actions for most of your sporterizing projects because they have a tendency to be a little weaker and take more work to bring about the desired effect. However, if the customer has one and you can work with it, by all means go ahead.

You can get a 98 that has a small ring up front. Around the time of World War I, they were trying to build rifles that were lighter in weight for some of their mountain troops, bicycle troops, and artillery. They’re a standard 98 action, but the front receiver is smaller in diameter where the barrel screws in. However, since it is smaller, you don’t want to open up your chamber to build a magnum with that small ring. You want a large ring 98 to build a magnum.


While we’re talking about magnums, let’s go into more detail on performing those conversions.

Starting with a large ring 98, you’ll have to open the bolt face, because the .30-06, 8mm, and 7mm case head sizes are smaller than the magnums. You have to open that bolt face so the larger diameter rim can slide up and center on the bolt face.

You’ll also have to alter the extractor by trimming its inside diameter large enough to allow the larger diameter case to slide up underneath it. One of the advantages of the Mauser that purists love is the full length, non-rotating claw extractor. This allows its famous “controlled feed.” This means that the cartridge feeds up out of the magazine and is captured on the face of the bolt by the extractor. The advantage is ultra reliable “straight into the chamber” feeding, and the ability to chamber a cartridge with the rifle held in any position imaginable. This reliability is a great comfort when hunting game that bites back.

"Minimalist" '98 conversion. Note bolt handle and modified and refinished military stock.

“Minimalist” ’98 conversion. Note bolt handle and modified and refinished military stock.

Next you’re going to alter the feed rails in the receiver. The magazine doesn’t have feed lips at its top, it fits up into the bottom of the receiver and the cartridges are pressed against the underside of the feed rails in the receiver by the magazine follower. Depending on which magnum cartridge you go with, you may be able to modify the existing magazine follower, but there are aftermarket magnum followers available. I always try to go with the least expensive one. If the military one works, there’s no need to spend money on something you don’t need. Make sure the cartridges snap down into the magazine and will stay under the rails on their corresponding side where they’re supposed to.

You may need to do just a little machining underneath the rails, or you may need to do a lot of machining, depending on the Mauser you have. For example, I built two .338 Win Mags. One needed about an hour-and-half worth of work in the mill, machining, filing, sanding, etc. The other needed about 15 minutes of filing and some quick sanding drum work. They were both .338 Win Mags—both ended up feeding perfectly, one just needed a lot more work to get there.

Heat Treatment

One thing I heavily emphasize is that, once you’ve done all the work on your action, you need to have it heat treated. There are several reasons. You don’t know how many rounds were fired through that gun. Was it on front-line service for five years and had a gazillion rounds shot through it? Eventually, it’s going to get tired and break. The metal is case-hardened mild steel. By heat treating it, you are going to reduce the possibility of having a problem. You’re making a new gun.

Another reason is because I usually lap the lugs and true the bolt face, which wears through that surface case hardening. This exposes the softer metal. As the cartridge detonates and is pressed back against the bolt face, the lugs are pushed back, stopped by their abutments in the receiver. If one is still hardened and the other soft, the hard one’s going to press into the soft one and you’re going to develop headspace.

It’s best to have this work done by a professional heat treatment specialist. We use Industrial Heat Treat in Salt Lake City, Utah.

Make sure to visit Guns and Gunsmiths regularly–Part 2 of this article will appear in the coming weeks!

7 Responses to Building A Custom Mauser Rifle–Part 1

  1. I have a 1917 (WWI) Danzig 98 action in an old .30-06 sporter. I’ve been told that this action is inferior to the later WWII 98’s because it’s made of softer steel. Is this true? Is it strong enough for heavy .30-06 loads?

  2. My custom 98 varmint rifle didn’t cost me much money.
    I used a
    Turkish mod t38 action, large ring with small barrel thread, about $30.00 dollars
    homemade trigger similar to some commercial triggers that I can adjust from about 10 ozs to over 3 lbs by changing springs, that is adjustable for engagement and over travel.
    I use take off Remington barrels, supposed to be new, that I turn and thread to fit the small barrel thread.
    I put this in a plastic stock made for a Win 70 that I alter.
    I also drill and tap for a scope.
    Altogether I have about $100 invested by doing this work myself, which makes for an inexpensive varmint and deer rifles.

  3. I built my Ex a .257 Roberts on a 1917 Danzig action used a barrel from Federal Firearms in Canonsburg a Tammany trigger and a F&R stock, and mounted a Bushnell 6x scope with a BRC. It wasn’t MOA but ground hogs never stood a chance out to about 350 yards. Gawd I miss that gun

  4. When you have a mauser receiver heat treated is that for case hardening only or for strength and what RC hardness should it be?

    • Steve. This article was posted some time ago and does not get many views anymore. You might have more luck posting your question in the gunsmithing forum.

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